Re: [configuration] Accessing from EL script

[Mark R. Diggory]

Emmanuel Bourg wrote:
Mark R. Diggory wrote:
For instance, storing :
config.add("a.b", z);
config.add("a.b.c", y);
config.add("a.b.c.d.e", x);
config.add("a.b.c.d.e.f", w);
${sessionScope.configAttribute.a.b} --> z
${sessionScope.configAttribute.a.b.c} --> y
${sessionScope.configAttribute.a.b.c.d.e} --> x
${sessionScope.configAttribute.a.b.c.d.e.f} --> w
but
${sessionScope.configAttribute.a.b.c.d}
   --> Map containing {"e",x; Map [x[ { "f",w } }

I'm not sure it works, if I understand well, the following EL:
${config.a.b.c}
translates into (through reflexion):
config.get("a").get("b").get("c");
but what is supposed to return the get("b") part ? the value of "a.b" 
that's "z" or the subset under "a.b" containing the "c", "c.d.e" and 
"c.d.e.f" elements ?

Emmanuel Bourg

Hmm, I get your point. That is a limiting factor, heres a possible solution:
In my example, we have the case that config.get("a") returns a nested 
structure of key --> Map pairs.
  
Map{
      "b",  Map {
                "c", Map {
                            "d", Map {
                                       "e", Map {
                                                    "f", value
                                                      }
                                             }
                                 }
                        }
            }

so that you can do:
config.get("a").get("b").get("c");
however, how do we get the object value for the case of "a.b.c" as 
opposed to the collection of its children. I suspect the answer is 
similar to that of "DOM" where an Element node has both Attributes and 
Children. So, a Map in this case has both a coercable Default Value 
(toString()) and Children.

[..] conotates "default value"
Map a = config.get("a");
   Map {
      "b",  Map [z] {                                            -----> 
a.get("b").toString() = z
                "c", Map [y] {                                   -----> 
a.get("b").get("c").toString() = y
                            "d", Map [NULL] {              -----> 
a.get("b").get("c").get("d").toString() = null
                                       "e", Map [x]{             -----> 
a.get("b").get("c").get("d").get("e").toString() = x
                                                    "f", w             
----> a.get("b").get("c").get("d").get("e").get("f").toString()  = w
                                                      }
                                             }
                                 }
                        }
            }

Unfortunately, JSTL's EL coercion isn't what I expected. I would expect 
Objects to be coerced to Strings using "toString()", then have the 
String coerced to Boolean, Number, char, etc... But Objects coerced to 
anything but string result in a coersion error. Which means that the 
results could never be used for EL arithmetic. That is something that 
could be taken up with the JSTL/EL folks though.

So for limited functionality, when a Map object is returned, it could be 
coerced to a String value using its "toString()" method at least for now.

So
${sessionScope.configAttribute.a.b} --> z
${sessionScope.configAttribute.a.b.c} --> y
${sessionScope.configAttribute.a.b.c.d.e} --> x
${sessionScope.configAttribute.a.b.c.d.e.f} --> w
but when ".b.c.d" is coerced
${sessionScope.configAttribute.a.b.c.d} --> null
as opposed to iterated over using JSTL which would be
${sessionScope.configAttribute.a.b.c.d}
  --> Map [NULL] {
           "e",x; Map [x] {
                         "f",w }
       }
-Mark

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